How to remove user-defined objects from memory?

Hi, let's say I have two classes A_Class() and B_Class(). The A_Class() is defined something like this:

classdef A_Class < handle
    properties
        B;
    end
    methods
        function obj = A_Class()
            obj.B{1} = B_Class();
            obj.B{2} = B_Class();
            obj.B{3} = B_Class();
        end
    end
end

I create an object of class A_Class(),

A = A_Class;

Then I run the following command:

length(A.B)

and the answer is 3, which is correct. However, when I delete the object A.B{3} using the command delete(A.B{3}) the object gets deleted but when I check for length of B using command length(A.B) the answer is still 3, why? When I try to access A.B{3} matlab tells me that it is an invalid or deleted object, but still gives an answer 3 for the length of A.B why? How can make the answer 2, which is the correct answer. This is frustrating, I tried clearing the handle A.B{3} but that does not help. Any help will be appriciated, thanks a lot in advance :)

Answer 1

[Guillaume]

Note that this has nothing to do with objects. You don't seem to be understanding cell arrays.

Your B is a cell array. A cell array is simply a container. When you ask matlab length(B) you ask the length of the container. You've created a container with 3 slots, therefore its length is 3. It doesn't matter what is in the slot, an object, a lump of coal, or nothing, the length of the container is unchanged. Note that {} affects the content of a slot, not a slot itself. You use () to interact with the container itself.

B = {[1 2 3], 'a lump of coal', B_class};  %a container of length 3, containing various things.
B{3} = [];  %replace the content of slot 3 with nothing. The container has still length 3
B(3) = [];  %delete slot 3 from the container, regardless of what's in it. length is now 2

[Robert U]

A = A_Class;
length(A.B)

ans = 3

A.B(3) = [];
length(A.B)

ans = 2

[Chaitanya Jha]

Perfect! Thank you so much. Can't believe I was thinking that was because of how class-object relationship in Matlab.